A Long Term Evolution (LTE) system includes an evolved packet core (EPC), an evolved NodeB (eNodeB), and user equipment (UE). The EPC is a core network part, and includes a mobility management entity (MME) that is responsible for signaling processing and a serving gateway (SGW) that is responsible for data processing. The eNodeB is connected to the EPC by using an S1 interface, eNodeBs are connected by using an X2 interface, and the eNodeB is connected to the UE by using a Uu interface.
An evolved universal terrestrial radio access network (E-UTRAN) includes eNodeBs and is responsible for implementing a radio-related function. An E-UTRAN protocol framework includes a user plane protocol and a control plane protocol. A user plane protocol stack includes a Packet Data Convergence Protocol (PDCP) layer, a Radio Link Control (RLC) layer, and a Media Access Control (MAC) layer.
Referring to FIG. 1, in the prior art, a data packet may be transmitted from a PDCP entity to an RLC entity. The RLC entity may include a transparent mode (TM), an unacknowledged mode (UM), and an acknowledged mode (AM). The RLC entity shown in FIG. 1 is an AM RLC entity.
For a carrier aggregation (CA) scenario of an ideal backhaul heterogeneous network (HetNet), an AM RLC entity may offload data packets to a macro eNodeB to which a primary cell (Pcell) belongs and a micro eNodeB to which a secondary cell (Scell) belongs, so as to separately send the data packets to user equipment (UE) by using the primary cell and the secondary cell, and improve data sending efficiency.
In an actual network, transmission between a Macro eNodeB and a Micro eNodeB is generally non-ideal backhaul transmission, and because a transmission delay between the Macro eNodeB and the Micro eNodeB is relatively long, performance of UE in a CA scenario of a non-ideal backhaul HetNet is affected.